Acetaldehyde (AcH), the initial metabolite of ethanol (EtOH) has been the subject of increasing interest recently because its high toxicity and biological activities may be involved in some of the most important effects of EtOH including hepatotoxicity, cardiomyophathy, euphoria, chemical dependence and, in very high levels, alcohol aversion. Blood AcH levels are elevated in some, but not all alcoholics and higher AcH levels are produced in their healthy non-alcoholic male relatives suggesting and inherited etiological factor. However, the exact role of AcH is uncertain because of difficulties in methods for analysis of AcH in biological fluids generated by 1) its high chemical reactivity causing binding and 2) non-enzymatic formation of AcH from EtOH during deproteinization of blood samples. A new method for measuring AcH in blood and other biological fluids using HPLC separation and analysis is being developed. The non-enzymatic conversion of EtOH to AcH which occurs in older methods during RBC precipitation is prevented by the addition of socium azide. Acetaldehyde is converted to its 2, 4-dinitrophenylhydrazine derivative for UV detection at 254 nM. The methods is sensitive to nanogram/ml concentrations of acetaldehyde in biological fluids. Further development of this novel method for acetaldehyde with increased sensitivity over existing methods is proposed and a comparison to currently used methods will be conducted. Application of the improved method will be made to the measurement of AcH levels in humans and animals. Two special objectives of the proposed research are the development of a method for low levels of AcH in saliva and the measurement of AcH in rats having a subcutaneous air pocket during chronic EtOH consumption. These tests are essential to further validate the role of AcH in alcohol actions and alcoholism.